1. Field of the Invention
The present invention relates to an optical device used for optical communication.
2. Description of the Related Art
FIG. 19 shows an example of an optical coupler using a Y-separation waveguide, which is a conventional optical device. A conventional optical coupler 206 has a configuration in which a Y-shaped core 203 is formed on a substrate 204. A first ingoing optical fiber 201 and a second ingoing optical fiber 202 are placed on one end face of the optical coupler 206, and an outgoing optical fiber 205 is placed on the other end face thereof. The first and second ingoing optical fibers 201 and 202 and the outgoing optical fiber 205 respectively are placed in the vicinity of the end faces of the Y-shaped core 203.
Light is incident upon the optical coupler 206 via the first and second ingoing optical fibers 201 and 202. The respective light beams propagate through the core 203 and are coupled to be output so as to propagate through the outgoing optical fiber 205. The light beams to be coupled need to be in the same phase.
On the other hand, if the ingoing side and the outgoing side of the above-mentioned optical coupler are used in a reverse manner, the optical coupler functions as an optical separator. That is, if incident light is allowed to propagate through the outgoing optical fiber 205, the light is separated to be incident upon the first and second ingoing optical fibers 201 and 202, respectively.
In an optical device such as the above-mentioned optical coupler 206, in order to couple light among the core 203, the first and second ingoing optical fibers 201 and 202, and the outgoing optical fiber 205, it is required to conduct the alignment of optical axes and matching in a mode shape with high precision. Therefore, skilled labor is required for assembling the device. In addition, a coupling angle of the optical coupler 206 is small, so that the device cannot be miniaturized.
Furthermore, in a conventional optical device, a light transmitting/receiving module for WDM (wavelength division multiplexing) that couples a plurality of light beams or separates light is constituted by using an optical waveguide, a multi-layer filter, and the like. This increases the number of components, making it difficult to achieve a low cost.
In order to solve the above-mentioned problems, recently, producing an optical fiber by using a photonic crystal has drawn attention. For example, JP 11(1999)-271541 A discloses a wavelength separating circuit using a photonic crystal of a two-dimensional triangular lattice.
In the present specification, the term xe2x80x9cphotonic crystalxe2x80x9d refers to an artificial multi-dimensional periodic structure substantially having a period of a light wavelength. It is known that light with a predetermined frequency, which propagates through a photonic crystal, is deflected. More specifically, a photonic crystal has wavelength dispersion characteristics with a strong deflection that is not found in general optical crystal. Due to the characteristics, a photonic crystal is used for an optical device such as a device for WDM.
The wavelength separating circuit using a photonic crystal disclosed in JP 11(1999)-271541 A allows light to be incident thereupon by placing a light incident surface to a photonic crystal in a non-vertical direction to a lattice vector or by tilting the light incident surface with respect to an incident surface perpendicular to the lattice vector direction. This is because the above-mentioned wavelength separating circuit uses a photonic crystal with a high symmetry such as a tetragonal lattice and a triangular lattice. This configuration requires a higher processing precision of an incident angle of an optical system in the course of production of a photonic crystal, making modularization difficult.
Furthermore, in a conventional optical device using a photonic crystal, such as an optical fiber, only two kinds of wavelengths are used, and in an optical device for power separation, only one kind of wavelength is used.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical device, such as an optical filter for WDM and an ADD-DROP apparatus for separating at least three kinds of wavelengths, a separator for WDM for power-separating at least two wavelengths, and an optical coupler, which can be produced easily and miniaturized, and a method for producing a photonic crystal.
An optical device of the present invention includes: a complex photonic crystal in which a plurality of materials with different refractive indices are placed periodically, whereby a plurality of photonic crystals with a periodic refractive index distribution are arranged in a column in a direction of a common primitive lattice vector; an ingoing optical waveguide for allowing light to be incident upon the complex photonic crystal; and an outgoing optical waveguide for receiving light output from the complex photonic crystal. Because of this, an optical device used for optical communication can be produced easily.
Furthermore, in each of the photonic crystals, at least one of a refractive index of the plurality of materials and a periodic structure of a refractive index thereof may be varied on the photonic crystal basis.
Furthermore, each of the photonic crystals may be a two-dimensional photonic crystal.
Furthermore, preferably, two primitive lattice vectors of each of the photonic crystals are parallel to each other, and either one of the two primitive lattice vectors is matched with an optical axis. Because of this, light (selection light) is deflected in a photonic crystal and can be controlled.
Furthermore, the photonic crystal may be interposed between a first cladding and a second cladding.
Furthermore, preferably, a refractive index of at least one of the first cladding and the second cladding is 1. Because of this, the cladding can be made of air, which reduces the number of components.
Furthermore, preferably, the above-mentioned optical device includes a groove for positioning the ingoing optical waveguide and the outgoing optical waveguide that are optical fibers. Because of this, it is possible to position an optical fiber easily without alignment of optical axes and matching in a mode shape with high precision.
Furthermore, the groove may be integrated with each of the photonic crystals directly or indirectly.
Furthermore, preferably, the complex photonic crystal is covered with an air-tight case completely, and an inside of the air-tight case is filled with a gas or evacuated. Because of this, the refractive index of the columnar materials that are made of a gas is not varied by a change in an external environment. This allows an optical device with good stability to realized.
Furthermore, preferably, each of the photonic crystals has a refractive index period determined by a specific wavelength of light that is deflected in each of the photonic crystals, and the specific wavelength is varied depending upon each of the photonic crystals. Because of this, light with a plurality of wavelengths can be dealt with.
Furthermore, an order in a column of each of the photonic crystals may be determined based on the specific wavelength of each of the photonic crystals.
Furthermore, preferably, each of the photonic crystals has a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between two primitive lattice vectors of the photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, the photonic crystals are arranged in a column in a direction of a first primitive lattice vector that is one of the two primitive lattice vectors to form the complex photonic crystal. The ingoing optical waveguide includes a first ingoing optical waveguide that is placed on a photonic crystal in a first stage of the complex photonic crystal, for allowing light other than light having a specific wavelength of each of the photonic crystals to be incident upon the complex photonic crystal in the direction of the first primitive lattice vector, and a second ingoing optical waveguide that is placed on each of the photonic crystals, for allowing light having a specific wavelength to be incident upon each of the photonic crystals, and the outgoing optical waveguide is placed so as to have the same optical axis as that of the first ingoing optical wave guide. Because of this, an optical device can be realized that is produced easily and enables light having a plurality of wavelengths to be coupled in an arbitrary order.
Furthermore, the second ingoing optical waveguide may be placed on a side of each of the photonic crystals.
Furthermore, preferably, end faces of the photonic crystals increase in size successively, and the second ingoing optical waveguide is placed on the end face of each of the photonic crystals. Because of this, the second ingoing optical waveguide is not placed on the photonic crystal in a lateral direction, so that an optical device with a small width can be realized.
Furthermore, each of the photonic crystals at least other than the photonic crystal in a final stage has a mirror having a predetermined angle with respect to an outgoing end face connected in a column on a part of the end face, and light from the second ingoing optical waveguide is reflected from the mirror and is incident upon the photonic crystal in a subsequent stage.
Furthermore, preferably, each of the photonic crystals has a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between two primitive lattice vectors of the photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, the photonic crystals are arranged in a column in a direction of a first primitive lattice vector that is one of the two primitive lattice vectors to form the complex photonic crystal. The ingoing optical waveguide allows light to be incident upon the complex photonic crystal in the direction of the first primitive lattice vector, and the outgoing optical waveguide includes a first outgoing optical waveguide that is placed on a photonic crystal in a final stage of the complex photonic crystal, for receiving light output in the direction of the first primitive lattice direction, and a second outgoing optical waveguide placed on each of the photonic crystals. Because of this, an optical device can be realized, which is produced easily and allows light with a plurality of wavelengths to be separated in an arbitrary order.
Furthermore, the second outgoing optical waveguide placed on each of the photonic crystals receives light with the specific wavelength, which is deflected in the photonic crystal and output therefrom.
Furthermore, a lattice constant of each of the photonic crystals may be 0.4 to 0.6 times the specific wavelength of each of the photonic crystals.
Furthermore, the second outgoing optical waveguide may be placed on a side of each of the photonic crystals.
Furthermore, preferably, only the second outgoing optical waveguide connected to the photonic crystal in the final stage of the complex photonic crystal is placed on an end face of the photonic crystal. Because of this, the length of the photonic crystal in the final stage can be made small, so that the entire optical device can be miniaturized.
Furthermore, preferably, end faces of the photonic crystals decrease in size successively, and the second outgoing optical waveguide is placed on the end face of each of the photonic crystals. Because of this, an optical device with a small width can be realized.
Furthermore, each of the photonic crystals at least other than the photonic crystal in a first stage has a mirror, which has a predetermined angle with respect to an ingoing end face connected in a column, on a part of the end face, and the second outgoing optical waveguide is provided at a position so as to receive light reflected from the mirror, which has the specific wavelength and is output from the photonic crystal in a previous stage.
Furthermore, another optical device of the present invention includes: a second complex photonic crystal in which a plurality of first complex photonic crystals, each including a first photonic crystal and a second photonic crystal connected to each other, are connected in a column so that each boundary face is placed on the same face; an ingoing optical waveguide for allowing light to be incident upon the second complex photonic crystal; and an outgoing optical waveguide for receiving light output from the second complex photonic crystal. Because of this, an optical device can be produced easily, and the cost thereof can be reduced.
Furthermore, the second complex photonic crystal may be interposed between a first cladding and a second cladding.
Furthermore, a refractive index of at least one of the first cladding and the second cladding may be 1.
Furthermore, the above-mentioned optical device may include a groove for positioning the ingoing optical waveguide and the outgoing optical waveguide that are optical fibers.
Furthermore, the groove may be integrated with the second complex photonic crystal directly or indirectly.
Furthermore, the second complex photonic crystal may be covered with an air-tight case completely, and an inside of the air-tight case may be filled with a gas or evacuated.
Furthermore, preferably, the first photonic crystal and the second photonic crystal have a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between respective primitive lattice vectors of the first photonic crystal and the second photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, a first primitive lattice vector of the first photonic crystal and a first primitive lattice vector of the second photonic crystal are parallel to each other, and are parallel to a boundary face where the first photonic crystal and the second photonic crystal are bonded to each other, a lattice structure of the first photonic crystal is symmetrical to a lattice structure of the second photonic crystal with respect to the boundary face, and the outgoing optical waveguide is placed on an end face of the first complex photonic crystal in a final stage of the second complex photonic crystal. Because of this, an optical device can be realized, which is produced easily and allows light with a plurality of wavelengths to be coupled in an arbitrary order.
Furthermore, a length of each of the first complex photonic crystals may be set so that light beams with wavelengths specific to each of the first photonic crystals and each of the second photonic crystals, which are deflected therein and output therefrom, are output from end faces of each of the first photonic crystals and each of the second photonic crystals.
Furthermore, a length of each of the first complex photonic crystal is set so that light beams with wavelengths specific to each of the first photonic crystal and each of the second photonic crystal, which are deflected therein, cross each other at an end of each of the photonic crystals.
Furthermore, preferably, each of the first photonic crystal and the second photonic crystal has a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between respective primitive lattice vectors of the first photonic crystal and the second photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, a first primitive lattice vector of the first photonic crystal and a first primitive lattice vector of the second photonic crystal are parallel to each other, and are parallel to a boundary face where the first photonic crystal and the second photonic crystal are bonded to each other, a lattice structure of the first photonic crystal is symmetrical to a lattice structure of the second photonic crystal with respect to the boundary face, and the outgoing optical waveguide includes a first outgoing optical waveguide placed on the first photonic crystal in a final stage of the second complex photonic crystal, for receiving light output in a direction of the first primitive lattice vector, and a second outgoing optical waveguide placed on each of the first complex photonic crystals, for receiving light beams with wavelengths specific to each of the first photonic crystals and each of the second photonic crystals, which are deflected therein and output therefrom. Because of this, an optical device can be realized, which is produced easily and allows light with a plurality of wavelengths to be separated in an arbitrary order.
Furthermore, a difference between a refractive index of the first material and a refractive index of the columnar materials may be at least 1.0.
Furthermore, the first material may be made of a polymer, and the columnar materials may be made of a gas.
Furthermore, a lattice constant of each of the first photonic crystal and the second photonic crystal may be 0.4 to 0.6 times the specific wavelength.
Furthermore, a cross-sectional shape of the columnar materials may be a circle with a radius of 0.08 to 0.3 times the specific wavelength.
Still another optical device of the present invention includes: a first photonic crystal having a first ingoing optical waveguide placed on an ingoing end face and a first outgoing optical waveguide and an optical waveguide for DROP placed on an outgoing end face; and a second photonic crystal having a second ingoing optical waveguide and an optical waveguide for ADD placed on an ingoing end face and a second outgoing optical waveguide placed on an outgoing end face. Furthermore, the first outgoing optical waveguide and the second ingoing optical waveguide, or the first ingoing optical waveguide and the first outgoing optical waveguide are connected to each other, the first photonic crystal and the second photonic crystal have a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between respective primitive lattice vectors of the first photonic crystal and the second photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, light incident upon the optical waveguide for DROP has a specific wavelength so as to be deflected in the first photonic crystal, and light incident upon the second photonic crystal from the optical waveguide for ADD has a specific wavelength so as to be deflected in the second photonic crystal. Because of this, an optical device can be realized that is capable of taking only a particular wavelength and adding the wavelength again in the course of multiplex transmission of wavelengths.
Furthermore, preferably, light that is deflected in the first photonic crystal and is incident upon the optical waveguide for DROP is processed to be incident upon the optical waveguide for ADD. Because of this, an optical device can be realized that is capable of taking only a particular wavelength and adding it again after modifying it in the course of multiplex transmission of wavelengths.
Furthermore, the first ingoing optical waveguide, the second ingoing optical waveguide, the first outgoing optical waveguide, the second outgoing optical waveguide, the optical waveguide for ADD, and the optical waveguide for DROP may be optical fibers.
Furthermore, still another optical device of the present invention includes: a complex photonic crystal having a configuration in which a waveguide portion is interposed between a first photonic crystal and a second photonic crystal; an ingoing optical waveguide placed on one end face of the complex photonic crystal; and three outgoing optical waveguides placed on the other end face of the complex photonic crystal. The first photonic crystal and the second photonic crystal have a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between respective primitive lattice vectors of the first photonic crystal and the second photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, a direction of a first primitive lattice vector of the first photonic crystal, a direction of a first primitive lattice vector of the second photonic crystal, a direction of an optical axis of the ingoing optical waveguide, a boundary face between the first photonic crystal and the waveguide portion, and a boundary face between the second photonic crystal and the waveguide portion are parallel to each other, a lattice structure of the first photonic crystal is symmetrical to a lattice structure of the second photonic crystal with respect to the waveguide portion, and an optical axis of the ingoing optical waveguide is in the waveguide portion and is identical with an optical axis of one of the outgoing optical waveguides, and optical axes of the other two outgoing optical waveguides are placed so as to be symmetrical to the optical axis of the ingoing optical waveguide. Because of this, an optical separator can be realized that is produced easily and is capable of separating light into three light beams.
Furthermore, preferably, a width of the waveguide portion is smaller than a core diameter of the ingoing optical waveguide. Because of this, an optical separator capable of separating light into three light beams can be realized.
Furthermore, still another optical device of the present invention includes: a complex photonic crystal having a configuration in which a waveguide portion is interposed between a first photonic crystal and a second photonic crystal; three ingoing optical waveguides placed on one end face of the complex photonic crystal; and an outgoing optical waveguide placed on the other end face of the complex photonic crystal. The first photonic crystal and the second photonic crystal have a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between respective primitive lattice vectors of the first photonic crystal and the second photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, a direction of a first primitive lattice vector of the first photonic crystal, a direction of a first primitive lattice vector of the second photonic crystal, a direction of an optical axis of the ingoing optical waveguide, a boundary face between the first photonic crystal and the waveguide portion, and a boundary face between the second photonic crystal and the waveguide portion are parallel to each other, a lattice structure of the first photonic crystal is symmetrical to a lattice structure of the second photonic crystal with respect to the waveguide portion, and an optical axis of one of the ingoing optical waveguides is in the waveguide portion and is identical with an optical axis of the outgoing optical waveguide, and optical axes of the other two ingoing optical waveguides are placed so as to be symmetrical to the optical axis of one of the ingoing optical waveguides. Because of this, a 3-coupler that is produced easily can be realized.
Furthermore, preferably, the ingoing optical waveguide and the outgoing optical waveguide are optical fibers. Because of this, the ingoing optical waveguide and the outgoing optical waveguide can be bent, easily dealt with, and set.
Furthermore, preferably, a width of the waveguide portion is smaller than a core diameter of the ingoing optical waveguide. Because of this, a 3-coupler can be realized.
Furthermore, still another optical device of the present invention includes: a complex photonic crystal in which a first photonic crystal is bonded to a second photonic crystal; a first ingoing optical waveguide for allowing light to be incident upon the first photonic crystal of the complex photonic crystal; a second ingoing optical waveguide for allowing light to be incident upon the second photonic crystal of the complex photonic crystal; and an outgoing optical waveguide for receiving light output from the complex photonic crystal. The first photonic crystal and the second photonic crystal have a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between respective primitive lattice vectors of the first photonic crystal and the second photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, a first primitive lattice vector of the first photonic crystal and a first primitive lattice vector of the second photonic crystal are parallel to each other, and are parallel to a boundary face where the first photonic crystal and the second photonic crystal are bonded to each other, a lattice structure of the first photonic crystal is symmetrical to a lattice structure of the second photonic crystal with respect to the boundary face, and light beams specific to each of the first photonic crystals and each of the second photonic crystals, which are deflected therein and output therefrom, cross each other on an end face of the complex photonic crystal. Because of this, an optical coupler that is produced easily can be realized.
Furthermore, still another optical device of the present invention includes: a photonic crystal; a first ingoing optical waveguide and a second ingoing optical waveguide for allowing light to be incident upon the photonic crystal; and an outgoing optical waveguide for receiving light output from the photonic crystal. The photonic crystal has a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between primitive lattice vectors of the photonic crystal is larger than 60xc2x0 and smaller than 90xc2x0, the first ingoing optical waveguide and the second ingoing optical waveguide allow light to be incident in a direction of a first primitive lattice vector of the photonic crystal, and an optical axis of the first ingoing optical waveguide is identical with an optical axis of the outgoing optical waveguide. Because of this, an optical separator that is produced easily can be realized.
Furthermore, the first ingoing optical waveguide, the second ingoing optical waveguide, and the outgoing optical waveguide may be optical fibers.
Furthermore, a distance between the first ingoing optical waveguide and the second ingoing optical waveguide may be proportional to a length of the photonic crystal.
Furthermore, a method for producing a photonic crystal of the present invention includes: irradiating a single ion at desired positions for placing columnar materials of a first material formed on a substrate, thereby forming a track in the first material; and soaking the substrate and the first material in an alkaline solution to erode the track, thereby forming columnar holes. Because of this, a photonic crystal can be configured easily.
Furthermore, at least one single ion may be irradiated.
Furthermore, preferably, the energy of the single ion is 1 MeV or more. Because of this, an ion penetrates the first material deeply.
Furthermore, the columnar holes may be filled with a material having a refractive index different from that of the first material.
Furthermore, the first material may be made of a polymer material, and the columnar holes may be filled with a gas.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.